//! Safe Rust DBMS for DBOS
//! 
//! 这是 DBOS 的安全部分，使用 Safe Rust 实现
//! 通过 FFI 与 Cz Exokernel 交互

#![no_std]
#![forbid(unsafe_code)]  // 禁止 unsafe 代码

extern crate alloc;
use alloc::vec::Vec;
use alloc::string::String;

/// Exokernel API（由 Cz 提供）
#[repr(C)]
pub struct ExokernelAPI {
    pub alloc_page: extern "C" fn(size: usize) -> *mut u8,
    pub free_page: extern "C" fn(page: *mut u8) -> bool,
    pub disk_read: extern "C" fn(block: u64, buf: *mut u8, len: usize) -> bool,
    pub disk_write: extern "C" fn(block: u64, buf: *const u8, len: usize) -> bool,
    pub net_send: extern "C" fn(packet: *const u8, len: usize) -> bool,
    pub net_recv: extern "C" fn(buf: *mut u8, len: usize) -> isize,
}

/// 全局 Exokernel API 实例
static mut EXOKERNEL_API: Option<&'static ExokernelAPI> = None;

/// 初始化 DBMS
#[no_mangle]
pub extern "C" fn dbms_init(api: &'static ExokernelAPI) -> bool {
    unsafe {
        EXOKERNEL_API = Some(api);
    }
    true
}

/// 数据库实例
pub struct Database {
    storage: StorageEngine,
    // transaction_manager: TransactionManager,
    // query_executor: QueryExecutor,
}

impl Database {
    pub fn new() -> Self {
        Self {
            storage: StorageEngine::new(),
        }
    }
    
    /// 执行 SQL 查询
    pub fn execute_query(&self, _sql: &str) -> Result<QueryResult, DBError> {
        // TODO: 实现 SQL 解析和执行
        Ok(QueryResult {
            rows: Vec::new(),
            affected_rows: 0,
        })
    }
    
    /// 开始事务
    pub fn begin_transaction(&self) -> Result<Transaction, DBError> {
        Ok(Transaction { id: 0 })
    }
    
    /// 提交事务
    pub fn commit(&self, _tx: Transaction) -> Result<(), DBError> {
        Ok(())
    }
}

/// 存储引擎
pub struct StorageEngine {
    // pages: Vec<Page>,
}

impl StorageEngine {
    pub fn new() -> Self {
        Self {
            // pages: Vec::new(),
        }
    }
    
    /// 读取页
    pub fn read_page(&self, _page_id: u64) -> Result<Page, DBError> {
        // 通过 Exokernel API 读取磁盘
        Ok(Page {
            id: 0,
            data: Vec::new(),
        })
    }
    
    /// 写入页
    pub fn write_page(&mut self, _page: &Page) -> Result<(), DBError> {
        // 通过 Exokernel API 写入磁盘
        Ok(())
    }
}

/// 页
pub struct Page {
    pub id: u64,
    pub data: Vec<u8>,
}

/// 查询结果
#[repr(C)]
pub struct QueryResult {
    pub rows: Vec<Row>,
    pub affected_rows: u64,
}

/// 行
#[repr(C)]
pub struct Row {
    pub columns: Vec<Column>,
}

/// 列
#[repr(C)]
pub struct Column {
    pub name: String,
    pub value: Value,
}

/// 值
#[repr(C)]
pub enum Value {
    Int(i64),
    Float(f64),
    String(String),
    Null,
}

/// 事务
pub struct Transaction {
    pub id: u64,
}

/// 数据库错误
#[derive(Debug)]
pub enum DBError {
    IOError,
    ParseError,
    TransactionError,
    OutOfMemory,
}

/// C FFI 导出：执行查询
#[no_mangle]
pub extern "C" fn dbms_execute_query(
    _sql: *const u8,
    _sql_len: usize,
    _result: *mut QueryResult,
) -> bool {
    // TODO: 实现
    false
}

/// C FFI 导出：开始事务
#[no_mangle]
pub extern "C" fn dbms_begin_transaction() -> u64 {
    // TODO: 实现
    0
}

/// C FFI 导出：提交事务
#[no_mangle]
pub extern "C" fn dbms_commit_transaction(_tx_id: u64) -> bool {
    // TODO: 实现
    false
}

/// C FFI 导出：回滚事务
#[no_mangle]
pub extern "C" fn dbms_rollback_transaction(_tx_id: u64) -> bool {
    // TODO: 实现
    false
}

// 测试模块
#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn test_database_creation() {
        let db = Database::new();
        assert!(db.execute_query("SELECT 1").is_ok());
    }
}
